1. Field of Invention
This invention relates to liquid crystal display control devices and liquid crystal display apparatus.
2. Description of Related Art
The liquid crystal display is becoming popular for it""s space saving characteristics and low power consumption in picture display devices. Research on liquid crystal displays is being done actively, and the performance of liquid crystal displays has improved remarkably in recent years.
Liquid crystals have a property of changing their molecular orientation when an electric field is applied. A vertical alignment-type liquid crystal is shown in FIGS. 5(a) and 5(b). FIG. 5(a) shows a liquid crystal of a vertical alignment-type liquid crystal when an electric field is not applied. FIG. 5(b) shows the same liquid crystal when an electric field is applied.
A negative dielectric anisotropic nematic liquid crystal molecule 2, sandwiched between a pair of electrodes 1, is oriented vertically with respect to the pair of electrodes 1 as shown in FIG. 5(a) when no voltage is applied to the electrodes 1. When a voltage is applied to the electrodes 1, the orientation of the nematic liquid crystal molecule 2 changes to horizontal relative to the electrode 1 as shown in FIG. 5(b). The liquid crystal illustrated in FIGS. 5(a) and 5(b) is called a vertical alignment type liquid crystal of an electric field effect-type.
Another type of liquid crystal is called a horizontal alignment liquid crystal of an electric field effect type. This type of liquid crystal molecule aligns in the horizontal direction when no voltage is applied to a pair of electrodes. When a voltage is applied to the electrodes, the liquid crystal molecule orientation changes to vertical relative to the electrodes. This type of liquid crystal aligns to an electric field orientation when a voltage is applied to the electrodes.
Liquid crystal displays using above-described electric field effect-type liquid crystal, include a pair of transparent electrodes and a pair of orientation films beneath the inner sides of the electrodes. The orientation film has a plurality of grooves and is arranged such that the directions of the grooves are different by 90 degrees from each other. Polarizing plates are disposed outside the transparent electrodes, respectively. The liquid crystal molecules are oriented by aligning to the grooves of the orientation film in the neighborhood of each orientation film. Between the orientation films, the liquid crystal molecules are twisted continuously by 90 degrees. The pair of polarizing plates controls the beam to pass through or be intercepted. A pair of polarizing plates can be arranged in the same direction, or in 90 degree direction, according to a design of the display apparatus.
Normally black systems employ intercepting beams when no voltage is applied, and passes through the beam when a voltage is applied. In contrast, normally white systems employ intercepting beams when a voltage is applied, and passes through the beam when no voltage is applied.
Presently, liquid crystal displays for notebook computers, normally white system with a horizontal alignment liquid crystal of an electric field effect-type are popular. For a projection display and a television display, it is important to have wide view-angle characteristics, normally black systems are becoming popular with a vertical alignment-type liquid crystal.
Liquid crystal displays are controlled by the supply voltage to an individual pixel. If a fixed voltage is applied to each pixel adopting the normally black system liquid crystal display, a fixed brightness is sure to be obtained on the liquid crystal display. If a fixed voltage is applied to each pixel adopting a normally white system liquid crystal display, a fixed darkness is sure to be obtained on the liquid crystal display. However, even if a fixed voltage is applied to a pixel, the brightness or the darkness of the pixel is not constant due to the effect of the darkness or the brightness of the surrounding pixels. In other words, the brightness or the darkness of a pixel is affected by voltages applied to the surrounding pixels. The phenomenon of having non-constant brightness or darkness regardless of the same supply voltage is called discrimination.
Recently, the size of pixels of liquid crystal displays has become smaller and smaller. As a result, controlling discrimination is becoming more important in order to obtain a good quality liquid crystal display.
FIGS. 6 and 7 show discrimination data measured on a conventional vertical alignment normally black-type liquid crystal display. FIG. 6 shows image patterns for measurements of discrimination. FIG. 7 shows the relationship between an applied voltage and a standardized mean brightness value of a pixel of the image patterns. Each image pattern has eight columns and plural rows and the same voltage is applied to the pixels in the same column. FIG. 6(a) is a xe2x80x9c1111xe2x80x9d pattern. All pixels are applied voltage. FIG. 6(b) is a xe2x80x9c1110xe2x80x9d pattern. Pixels in the left three columns are applied voltage and the pixels in the fourth column are not applied voltage. FIG. 6(c) is a xe2x80x9c1100xe2x80x9d pattern. Pixels in the left two columns are applied voltage and the pixels in the third and forth columns are not applied voltage. FIG. 6(d) is namedxe2x80x9c1000xe2x80x9d pattern. Pixels in the first column are applied voltage and the pixels in the second through forth columns are not applied voltage. FIG. 6(e) is namedxe2x80x9c0101xe2x80x9d pattern. Pixels in the second and fourth columns are applied voltage and the pixels in the first and third columns are not applied voltage. In this measurement, the brightness of the entire image is measured changing the applied voltage to each pixel.
The processing for measured brightness values of one pixel is standardized as follows. First, the number of pixels to which the voltage is applied is counted for each image pattern. Next, all the measured brightness values of all image patterns are standardized using the highest brightness value. The measured brightness value at 3900 mV voltage of the xe2x80x9c1111xe2x80x9d pattern is set to be the standard 1.0. Finally, the standardized brightness values are divided by the number of voltage-applied pixels and the standardized brightness value for each image pattern is calculated.
The x-axis in the graph of FIG. 7 is the voltage (mV) applied to a pixel, and the y-axis is the standardized brightness value of the pixel. The mean standardized brightness value of a pixel of the xe2x80x9c1111xe2x80x9d pattern is plotted by the symbol xe2x80x9c♦xe2x80x9d in this graph. Also the mean standardized brightness value of a pixel of the xe2x80x9c1110xe2x80x9d pattern is plotted by the symbol xe2x80x9c▪xe2x80x9d, the xe2x80x9c1100xe2x80x9d pattern is plotted by the symbol xe2x80x9cxcex94xe2x80x9d, the xe2x80x9c1000xe2x80x9d pattern is plotted by the symbol xe2x80x9cXxe2x80x9d, and the xe2x80x9c0101xe2x80x9d pattern is plotted by the symbol xe2x80x9c∘xe2x80x9d.
Originally, the mean standardized brightness value of each pixel is expected to be the same value as that of the xe2x80x9c1111xe2x80x9d pattern. However, because of discrimination, the mean standardized brightness value of a pattern having non-voltage applied pixels is lower than that of the xe2x80x9c1111xe2x80x9d pattern when the applied voltage is 200 mV and above. Moreover, the mean standardized brightness value of the xe2x80x9c1100xe2x80x9d pattern (FIG. 6(c)) is higher than that of the xe2x80x9c0101xe2x80x9d pattern (FIG. 6(e)), even though the total number of voltage applied pixels are equal. The mean standardized brightness value of the xe2x80x9c0101xe2x80x9d pattern (FIG. 6(e)) is almost equal to that of the xe2x80x9c1000xe2x80x9d pattern (FIG. 6(d)), even though the total number of voltage applied pixels are doubled.
It is understood that on a normally black type liquid crystal display, discrimination appears to have an influence of darkening a pixel by surrounding black pixels. Moreover, a pixel to which the voltage is applied is affected by the discrimination largely owing to the number of surrounding pixels to which no voltage applied.
The discrimination in normally black-type liquid crystal displays causes a white character in a black background to look like a thinner and darker character. The discrimination in normally white-type liquid crystal displays causes a black character in a white background to look like a thinner and brownish character. Moreover, because the influence degree of the discrimination is different for each pixel in the color liquid crystal display panel regardless of whether it is a normally black or white type, a pixel that must be originally an achromatic color might be displayed as a chromatic color.
The above-described phenomenon is not limited to a liquid crystal display apparatus. That is, a pixel value of each pixel might also be influenced by surrounding pixels, causing an input pixel value change to a quite different pixel value, in two dimensional image display devices.
This invention provides liquid crystal display control devices, which reduce influences of surrounding pixels by processing a pixel value. This invention also provides liquid crystal display apparatus, which display images processed by the liquid crystal display control device. In addition, this invention provides spatial filtering methods.
An exemplary embodiment of the liquid crystal display control devices according to this invention include a data input port at which pixel data of a plurality of pixels forming a two-dimensional image is input, and a liquid crystal display control device. The liquid crystal display performs processing and, particularly, associates a first element with a first pixel of the two-dimensional image; associates each of a plurality of second elements with respective ones of a plurality of second pixels surrounding the first pixel of the two-dimensional image; sets a coefficient for each second element, corresponding to a difference value between each second pixel value of each second pixel and a pixel value of the first pixel; multiplies the coefficient set for the second element of each second pixel by the difference value between the second pixel value of each second pixel and the pixel value of the first pixel; adds all of the multiplication results of the plurality of second pixels; generates a new processed pixel value corresponding to the first pixel; and sets the first pixel to one pixel of the plurality of pixels of the two-dimensional image and performs the above processing for each pixel of the two-dimensional image one-by-one.
An exemplary embodiment of the liquid crystal display apparatus according to this invention includes a data input port, an embodiment of the liquid crystal display control devices according to this invention, such as the above-described embodiment, and a display panel that displays the two-dimensional image based on processed pixel data obtained by the liquid crystal display control device.
An exemplary embodiment of the spatial filtering methods according to this invention include determining each difference value of a second pixel value of each of a plurality of second pixels subtracted from a first pixel value of a first pixel; setting a coefficient corresponding to each difference value determined by subtracting the second pixel value of each second pixel from the first pixel value of the first pixel, respectively; multiplying the coefficient set corresponding to each second pixel by the difference value determined by subtracting the second pixel value of each-second pixel from the first pixel value of the first pixel; generating a renewed first pixel value of the first pixel by adding the multiplication results of each of the second pixels; and selecting the first pixel in the two-dimensional image one-by-one.